1. Field of the Invention
The present invention relates to a novel image sensor device, herein referred to as a light emitting and image sensing device, and the apparatus in which it is used.
2. Description of the Related Art
An embodiment of a conventional image sensor, in this case a CMOS image sensor, is schematically illustrated in cross-section in FIG. 1. A microlens 30 focuses incident light, or photons 32, on a plurality of photodiodes 34 in a silicon substrate 36. Color filters 38 filter photons of specific wavelengths so that each of the photodiodes 34 collects photons within one of three ranges of wavelengths, corresponding to red, green and blue light.
An embodiment of a conventional active pixel element in a CMOS image sensor is illustrated in schematic view in FIG. 2. The active pixel element comprises a photodiode and an active pixel circuit indicated generally by reference numerals 34.2 and 40 respectively. The photodiode 34.2 provides a photosensor signal on conductor 42. The photosensor signal on conductor 42 is read out through a buffer transistor 44 onto a column bus 46 when a row select transistor 48 is activated. A reset transistor 50 operates to reset the photodiode 34.2 to a known state.
A schematic plan view of the conventional image sensor is illustrated in FIG. 3. The conventional image sensor comprises a matrix of rows and columns of pixel elements indicated generally by reference numeral 52. Each of the pixel elements contains a photosensing structure and corresponding support circuitry, such as the photodiode 34.2 and active pixel circuit 40, respectively, illustrated in FIG. 2.
There are many image sensor applications wherein a light source is required to illuminate a scene, or an object, so that the image sensor can capture one or more images. Examples of such applications include but are not limited to video surveillance, cell phones, digital cameras and digital video systems. During low ambient light level conditions the light source is necessary for an image to be captured at all.
An example of a conventional infrared video surveillance camera is given by U.S. Pat. No. 6,642,955 by Brent Midgley et al. Midgley describes a CCD type image sensor in a camera system that switches electronically between infrared radiation sensing and visible light sensing depending on ambient conditions. Furthermore, the camera in Midgley makes use of either incandescent or LED type illuminators. These illuminators are located external to the camera system, but may be in a camera system enclosure along with the CCD image sensor.
An example of a CMOS sensor used in cell phone is given by U.S. Pat. No. 6,730,900 by Hsish et al. in which is described a novel CMOS based active sensor array that, along with focusing optics, is preferably incorporated into a cellular phone camera for producing electronic images.
A disadvantage of the prior art is the lack of integration of a light source for image illumination with the image sensor. This has resulted in excessively large image sensor products for the applications listed above. In the case of the video surveillance camera, the illuminator is either in a separate enclosure altogether, or is mounted inside the camera system enclosure thereby increasing the size.
Another disadvantage of the lack of integration is the inability to take advantage of an illumination apparatus. In a cell phone, for example, where space is a constrained, it is often not feasible to include the illumination apparatus. In this situation, a cell phone camera can only be used in conditions where ambient light is sufficient for its operation.
Furthermore, another disadvantage of the prior art is that by lack of integration the power consumption of the above mentioned products and applications is excessively large.